The present invention relates to a method and a device for setting a gear ratio in a motor vehicle having distance and/or vehicle-speed adjustment.
Distance and/or vehicle-speed controllers can be, for example, also designated as adaptive cruise control systems (ACC).
An ACC system based on radar is discussed in SAE paper 961010 (SAE Technical Paper Series 961010, International Congress and Exposition, Detroit, Feb. 26-29, 1996, xe2x80x9cAdaptive Cruise Control Systemxe2x80x94Aspects and Development Trendsxe2x80x9d, Winner, Witte, Uhler, Lichtenberg, Robert Bosch GmbH). In this case, the radar sensor having multiple target capability is mounted at the front end of a motor vehicle, in order to determine distances from, and speeds relative to vehicles driving ahead. The data ascertained by the radar system are supplied to a control unit via a bus system. Using the transmitted radar data and the wishes of the driver, this control unit determines an appropriate acceleration request which, in turn, is transmitted to a longitudinal control unit. The longitudinal control unit controls actuators in accordance with the acceleration request of the control unit. These actuators can be the engine of the motor vehicle, the clutch, or the brakes of the motor vehicle. The corresponding control of the actuators produces a certain behavior of the motor vehicle, which, in turn, is fed back to the control unit, thus forming a control loop. Either the drive train or the brakes are activated as a function of the corresponding acceleration request. The estimated incline of the road is considered in this selection. In addition, the limitations, i.e., physical limitations of the drive train and the braking system must be known or appropriately calculated.
In combining an ACC system with an automatic transmission, it is believed that unnecessary occurrences of transmission downshifting that reduce the driving comfort should be prevented during ACC closed-loop control.
For example, in a motor vehicle having an Otto engine, the driver of the motor vehicle may operate the throttle valve of the engine directly. This results in a nonlinear accelerator-pedal engine-torque characteristic to which the driver may be accustomed. In the case of newer vehicles, the driver no longer selects the throttle-valve setting or the engine load directly, but rather, just his or her propulsion wish or the output torque of the engine or the power output of the engine. To this end, the accelerator-pedal positions are assigned different output engine torques, or assigned the engine power outputs, using an engine characteristics map. The gear ratio in automatic transmissions may be selected mainly as a function of the engine load (throttle-valve position) and the driving speed.
In order to maintain the nonlinear accelerator-pedal engine-torque characteristic when combining an engine control system, in which the throttle-valve position is no longer input by the accelerator, with a conventional transmission control system, the gears are shifted on the basis of a so-called xe2x80x9cvirtualxe2x80x9d accelerator-pedal value, instead of using the torque or power output desired by the driver. The xe2x80x9cvirtualxe2x80x9d accelerator-pedal value corresponds to the real accelerator-pedal value, at which the requested vehicle propulsion would be set. This may create a problem when the setpoint variable, e.g., a setpoint torque, input by the ACC system, is close to the maximum engine torque. In this range, a small change in the setpoint torque already leads to a large jump in the virtual accelerator-pedal value, whereupon the transmission control system changes gears spontaneously. This shifting of gears can be especially disturbing and uncomfortable when there is only a small difference in torque between the setpoint torque and the maximum engine torque. This phenomenon can be counteracted by limiting the inverse accelerator-pedal value, e.g., to 80%. Such a limitation can also help in the ACC case, but it may prevent rapid downshifting when this is really needed.
The present invention relates to a method and a device for setting a gear ratio of the transmission installed in the drive train of a motor vehicle, while a distance and/or vehicle-speed control system (ACC system) is activated. A setpoint variable, as a function of which at least the driving motor of the vehicle is controlled, is input while the distance and/or vehicle-speed control system is activated.
An exemplary embodiment of the present invention provides for limiting this setpoint variable or a value derived from this setpoint variable, in response to the existence of a first operating state (normal ACC operation). The gear ratio can then set as a function of the limited variable, or as a function of the limited value. The gear ratio can be set as a function of the setpoint variable, or as a function of the value, in response to the existence of a second operating state.
An exemplary embodiment of the present invention can prevent uncomfortable gear changes of the transmission during ACC operation, without hindering or delaying downshifting when sharp acceleration is desired.
In an exemplary embodiment of the present invention, the setpoint variable representing a setpoint value for the output torque or the power output of the vehicle engine can be provided. An actual quantity representing the instantaneous output torque or the instantaneous power output of the vehicle engine can then be ascertained. Then, the second operating state can exists when the actual quantity deviates from the setpoint variable in a specifiable manner. The second operating state can exist even when the setpoint variable exceeds the actual quantity by a specifiable, first threshold value.
In another exemplary embodiment of the present invention, for the existence of the second operating state, the absolute value of the actual quantity can be provided to exceed a specifiable, second threshold value. It is believed that this can effectively prevent instances of false activation.
In another exemplary embodiment of the present invention, the driver of the vehicle can input an accelerator-pedal value representing the position of the accelerator using an accelerator pedal that can be operated by him or her. An additional setpoint variable can be ascertained from the accelerator-pedal variable using a nonlinear, first engine characteristics map. This additional variable may represent the propulsion wish that can be specified by the driver.
During activation of the ACC system, a virtual accelerator-pedal value is ascertained, using a second engine characteristics map, from the setpoint variable originating at the ACC system. When the ACC system is not activated, a virtual accelerator-pedal value is ascertained from the additional setpoint variable (propulsion wish of the driver), using the second engine characteristics map. The second engine characteristics map can be laid out inversely to the first engine characteristics map. However, it can also be provided that the actual accelerator-pedal angle be taken directly.
Another exemplary embodiment of the present invention may also provide for the gear ratio being set as a function of the inverse accelerator-pedal value and for limiting the inverse accelerator-pedal.